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                [Bjoi2014]路径                </h1>
                <p>时间限制：10s&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  空间限制：256MB</p>			</div>
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                                <h3>题目描述</h3><p><p>&nbsp;<img src="../file/4531_0.png" width="255" height="206" alt="" /></p>
<div>在一个N个节点的无向图（没有自环、重边）上，每个点都有一个符号，</div>
<div>可能是数字，也可能是加号、减号、乘号、除号、小括号。你要在这个图上数</div>
<div>一数，有多少种走恰好K个节点的方法，使得路过的符号串起来能够得到一</div>
<div>个算数表达式。路径的起点和终点可以任意选择。</div>
<div>所谓算数表达式，就是由运算符连接起来的一系列数字。括号可以插入在</div>
<div>表达式中以表明运算顺序。</div>
<div>注意，你要处理各种情况，比如数字不能有多余的前导0，减号只有前面</div>
<div>没有运算符或数字的时候才可以当成负号，括号可以任意添加（但不能有空括</div>
<div>号），0可以做除数（我们只考虑文法而不考虑语意），加号不能当正号。</div>
<div>例如，下面的是合法的表达式：</div>
<div>-0/0</div>
<div>((0)+(((2*3+4)+(-5)+7))+(-(2*3)*6))</div>
<div>而下面的不是合法的表达式：</div>
<div>001+0</div>
<div>1+2(2)</div>
<div>3+-3</div>
<div>--1</div>
<div>+1</div>
<div>()</div>
<div></div></p><hr/><h3>输入格式</h3><p><div>第一行三个整数N,M,K，表示点的数量，边的数量和走的节点数。</div>
<div>第二行一个字符串，表示每个点的符号。</div>
<div>接下来M行，每行两个数，表示一条边连的两个点的编号。</div>
<div>1&le;N&le;20，0&le;M&le;N&times;(N-1)/2，0&le;K&le;30</div>
<div></div></p><hr/><h3>输出格式</h3><p><div>输出一行一个整数，表示走的方法数。这个数可能比较大，你只需要输出</div>
<div>它模1000000007的余数即可。</div>
<div></div></p><hr/><h3>样例输入</h3><pre>6 10 3
)(1*+0
1 2
1 3
1 4
2 3
3 4
2 5
3 5
3 6
4 6
5 6</pre><hr/><h3>样例输出</h3><pre>10
//一共有10条路径，构成的表达式依次是101, (1), 1+1, 1+0, 1*1, 1*0, 0+0,
0+1, 0*0, 0*1</pre><hr/><h3>提示</h3><p>没有写明提示</p><hr/><h3>题目来源</h3><p>鸣谢佚名上传</p>
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